字符串插入

在原有字符串基础上插入一段字符串

/// <summary>        /// 填充字符串        /// </summary>        /// <param name="originalStr">原始字符串</param>        /// <param name="index">要插入的位置</param>        /// <param name="value">值</param>        /// <returns></returns>        private string FillString(string originalStr, int index, string value)        {            string pre = originalStr.Substring(0, index - 1);            string hind = originalStr.Substring(index - 1);            return pre + value + hind;        }